Pressurized fuel cell systems wherein compressed air from turbocompressors is used on the cathode side of the fuel cell are known. U.S. Pat. No. 3,973,993, Bloomfield et. al., granted Aug. 10, 1976, discloses a pressurized fuel cell power plant wherein a turbocompressor is operated by passing moist cathode exhaust gas and reformer exhaust gas through the turbine side of the turbocompressor. At such times when the temperature of the fuel cell stack is to be reduced or prevented from rising, then some coolant steam will also be ducted into the cathode side of the stack and thence to the turbine.
U.S. Pat. No. 3,982,962, Bloomfield, granted Sept. 28, 1976, discloses a pressurized fuel cell power plant wherein the cathode side of the stack is provided with compressed air from a turbocompressor. The turbine on the turbocompressor is powered by steam from the stack cooling system. The steam is condensed to water after exiting the turbine.
Both of the aforesaid systems operate the turbine with a single fluid source which is generally sufficient for most operating conditions. There are some operating conditions, however, which require that more energy be inputted into the turbine. Such conditions may include high ambient operating temperatures which provide less dense air to be compressed, and/or the stack may be operating at less than full load thereby lowering the available energy in the cathode exhaust. Both of these conditions will require that extra energy be supplied to the turbocompressor so that it can compress the air to the preset constant for which it is designed. In the prior art systems, when such conditions occur, an auxiliary burner will be activated to supply the extra energy to the turbine. The auxiliary burner will be fueled by the raw fuel from whence the hydrogen is derived for the fuel cell anode side. It will be appreciated that the use of such an auxiliary burner adds expense to the system and is wasteful of total system energy since it requires consumption of fuel over and above that which is required by the stack for the electrochemical reaction.